Vitamine A (retinol) and its metabolite retinoic acid are required for the maintenance of epithelia. vitamin A-deficient animals develop squamous metaplastic lesions similar to those in premalignancy. Conversely, laboratory animals supplemented with vitamin A compounds have a lower incidence of neoplasia when exposed to carcinogens. Thus, there is an intense interest in retinoids (naturally occurring and synthetic compounds with vitamin A activity) as cancer chemopreventive agents. Yet little is known about the basic biochemistry and metabolism of vitamin A. The aims of this work are to identify the charged vitamin A metabolites in circulation and in selected tissues under physiological conditions; determine their precursors, and sites of syntheses; and assay their activities in two systems that measure the differentiation and anti-carcinogenic potency of retinoids. These goals will be accomplished with extraction procedures, high-performance liquid chromatography, and mass spectroscopy techniques developed in this lab for such studies. Furthermore, a sensitive assay to quantify retinoid-induced embryonal carcinoma (EC) cell differentiation will be set-up and used to: measure the differentiation activity of vitamin A metabolites, and study the structure/function relationship of retinoids. The EC cells will also be used to correlate viitamin A metabolism and vitamin A-induced differentiation. The rationale supporting such investigations are: mechanisms of vitamin A actions can be studied more easily when the compounds that ultimately function are known; knowledge of vitamin A metabolism could offer new insight into diseases such as epithelial cancer, and may lead to new approaches to disease prevention and treatment; understanding the structure/function relationships of vitamin A and its metabolites would provide knowledge useful in the design of new compounds with enhanced activity, improved therapeutic indices, or selective action. These studies will also provide insight and methodology that can be extended to: study synthesis of retinoic acid from retinol and its regulation; examine effectors of vitamin A homeostasis; investigate retinoid function; and examine the metabolism of therapeutically useful retinoids.